The Pinnipedia superfamily (walruses, seals, and sea lions), now considered to be part of Caniformia, are medium to large (to 6.5 m) aquatic mammals. Being homeothermic (warm-blooded) marine mammals, pinnipeds need a low surface area to body mass ratio. Otherwise, they would suffer from excessive heat loss due to water's high capacity for heat conduction. The body is usually insulated with a thick layer of fat called blubber and typically covered with hair. The digits are not separate, but connected by a thick web that forms flippers for swimming; thus, the forelimbs and hindlimbs are transformed into paddles.